As far as I know Banshee "allows" only for 140 to 160 mm Fork (with internal/external Headset) on the V2 Spitfire. A taller Fork is going to affect Warranty ...
Maybe it depends on the maximum A-to-C-heigth ...

I have test-ridden the Spitfire v2 with a Fox Float 34 27,5 160mm, which is 555m A-C, the same a-c a Float 170mm 26 would have. I like the feeling of the bike a lot and am planning to build up the bike with a 180mm FLoat, reduced to 170mm to reach the A-C 555mm.

The A-C for a 170mm 26 Float is just 10mm above the recommended A-C, for which banshee reports geometry, so I would think it is within tolerance what the frame can take. Ihave not found any infor on this topic on the Banshee webpage (fork height restriction).

Same here. I´m riding a BOS Deville 160 mm travel 26"-Fork with 650B-Wheels (A-to-C 545 mm), ZS-Angleset and the Geometry (neutral Flip-Chips) feels damn perfect for my terrain. Wouldn´t like it higher up front or need more travel.
If I were you I would ask Banshee what´s the maximum A-to-C-heigth for the Spitfire ...